That’s the monster mountain of money outside political groups collectively spent in October to fill the nation’s airwaves, scorch your phone lines and flood your mailbox with flyers that directly promote or attack federal candidates, according to a POLITICO analysis of federal campaign spending disclosures.

Leading the way were the Karl Rove-backed super PAC American Crossroads, its nonprofit sister group Crossroads GPS and pro-Mitt Romney super PAC Restore Our Future, which has been fueled by tens of millions of dollars from billionaires such as casino mogul Sheldon Adelson and Texas home builder Bob Perry.

The three groups together spent nearly $173 million last month on ads and other communications, with the bulk targeting President Barack Obama.

To put that in perspective: That’s nearly as much as the roughly $179 million that all outside together spent in September to promote or attack federal candidates.

In all, 57 different outside organizations — the majority of them conservative-leaning — spent at least $1 million in October to promote or attack federal political candidates.

All groups spent more than $526 million in total last month — a significant chunk of the $6 billion the Center for Responsive Politics predicts all federal-level candidates, parties and committees will spend during the 2012 election.

Among the organizations spending more than $5 million during October on independent expenditures — typically, ads or other mass communications that overtly support or oppose federal political candidates:

1) American Crossroads, $71.64 million, mostly in opposition to Obama and in support of Romney.

2) Restore Our Future, $51.64 million, all in opposition to Obama or in support of Romney.

7) Service Employees International Union committees, $17.8 million, in support of Obama and numerous Democratic congressional candidates and in opposition to Romney and numerous Republican congressional candidates.

8) National Rifle Association committees, $15.4 million, mostly in support of Romney and numerous Republican congressional candidates and in opposition to Obama and numerous Democratic congressional candidates.

14) League of Conservation Voters committees, $7.68 million, mostly in support of Obama and numerous Democratic congressional candidates and in opposition to Romney and numerous Republican congressional candidates.

16) Ending Spending Action Fund, $7.25 million, mostly in support of Romney and Republican Senate candidates including Flake and in opposition to Obama and Democratic Senate candidates including Bob Kerrey (Neb.) and Brown.

20) Planned Parenthood committees, $5.56 million, mostly in support of Obama and numerous Democratic congressional candidates and in opposition to Romney and numerous Republican congressional candidates.

21) Now or Never PAC, $5.33 million, mostly in opposition to several Democratic congressional candidates including Sen. Jon Tester (Mont.), Richard Carmona (Ariz.), Brown and Duckworth and in support of Akin.